Hello,
We want to use straw balls in a wall,
We obtain the moisture storage function from the CSTB (France)
RH Kg/m3
0 0
0.1 2.6
0.3 6.1
0.6 9.8
0.8 12
0.98 33
1 100
a bulk density of 100 kg/m3
a porosity of 0.88 m3/m3
a heat capacity of 2000 J/kg.K
a heat conductivity dry 0.045 W/m.K
a diffusion resistance factor dry of 2.5
a heat conductivity, moisture dependent :
RH W/m.K
0 0.045
100 0.046
500 0.048
however we have a problem to estimate liquid transport coefficients,
As a rough approximation
We consider that with a porosity of 0.88 and only 100 kg/m3 of water at the free saturation, moreover with a little influency of RH on the heat conductivity and fibers oriented vertically.
The straw contain a lot of big pores and thus we could neglect the liquid transport coefficients, we consider that the flow is only diffusive (we are under 85% RH)
We keep in mind that if we do that the water content profil should be a little more flat than wufi results, due to redistribution.
What do you think about this assumption.
Thanking you by advance.
Greetings.
Straw,
Re: Straw,
Hi Raymond,Raymond wrote:The straw contain a lot of big pores and thus we could neglect the liquid transport coefficients, we consider that the flow is only diffusive (we are under 85% RH)
when the measurements done on straw-bale walls on our field-test site were to be compared with WUFI calculations, liquid transport in the straw was neglected in the calculations. The report says (p. 227):
"Since it can be assumed that liquid transport within a straw bale is so low that it has negligible effect on the moisture balance of the wall assembly, the liquid transport coefficients for suction and redistribution have not been taken into account in the calculations."
The comparison of measured and calculated temperature and moisture curves (diagram 10-22, p. 270) shows that measurement (black) and calculation (blue) agree very well, so that ignoring liquid transport appears indeed justified.
Kind regards,
Thomas